The rescue of a U.S. aid worker and a Danish colleague held hostage since October was carried out by Navy SEALs from the unit that killed Osama bin Laden.

Reporting from Washington and Mogadishu, Somalia — The Navy SEALs parachuted into the darkness, landing more than a mile from their objective: a small bush camp in north-central Somalia where an American aid worker and a Danish colleague were being held captive.

The commandos, several dozen in all, shed their chutes and moved quietly through the brush.

The compound had been under secret U.S. surveillance for weeks after an intelligence tip had signaled the whereabouts of the hostages, 32-year-old Ohio native Jessica Buchanan and 60-year-old Poul Thisted.

But investigators believed that Buchanan's health was failing and that she might suffer kidney failure. "We were told that she was not well and, left untreated, her condition could be life threatening," said a senior U.S. official.

About 2 a.m. Wednesday, the SEALs stormed the kidnappers' compound. In the ensuing firefight, they killed nine people and rescued the pair without injury.

The hostages and SEALs were picked up by helicopters, which flew to an airstrip at the Somali town of Galkayo, 60 miles north of the encampment. There the hostages were transferred to a U.S. military plane and flown to Djibouti.

Pentagon officials defended the decision to kill the hostage takers, arguing that they were armed and that explosives were found at the camp. The SEALs could have taken prisoners, but they were operating under rules of engagement that permitted use of deadly force if their lives or those of the hostages were threatened.

The dramatic rescue, by SEALs from the same special operations unit that killed Osama bin Laden in his Pakistan hideout in May, reflects how much has changed about U.S. capabilities in Somalia. In 1993, the U.S. military retreated from a failed peacekeeping mission after losing 18 Americans and two Black Hawk helicopters in a fierce battle in the capital, Mogadishu.

Only after the Sept. 11, 2001, terrorist attacks did the Pentagon return to Somalia and other countries in the region, deploying surveillance drone aircraft, special operations units and warships off the coast. The goal was to keep tabs on Islamist militants who have seized control of much of Somalia, and armed pirates who regularly hijack oil tankers and other ships and their crews for ransom off its coast.

An armed gang abducted Buchanan and Thisted in October in Galkayo, a bustling city of half a million people. The two were working for the Danish Refugee Council, a humanitarian aid group that helps clear minefields, aids maimed victims and assists refugees, the legacy of Somalia's years of lawlessness and civil war.

That same month, militants from the Shabab, an Islamic militant group that has carried out a violent campaign against the weak transitional government in Mogadishu, seized the Danish Refugee Council's offices and those of 15 other groups operating in southern Somalia, halting aid efforts in many areas.

U.S. investigators concluded early on that the men who kidnapped Buchanan and Thisted were criminals trying to make money from ransom, not Shabab militants or pirates.

At first, there were promising signs that the hostages' ordeal might be short. Local clan leaders denounced the abduction, and supporters organized demonstrations demanding their freedom. FBI agents investigating the kidnapping of the U.S. citizen were cautiously optimistic.

A team of hostage negotiators based out of the FBI's New York field office advised Buchanan's family and officials from the Danish Refugee Council, who had made contact with the kidnappers via sympathetic Somali clan leaders.

But the negotiations came to nought. Then in mid-January, the FBI received intelligence that the aid workers were under guard near the village of Hiimo Gaabo, 60 miles south of Galkayo.

Thisted, who had studied anthropology and education in Denmark, had worked in East Africa for more than a decade and had managed explosives safety programs in Somalia for the nonprofit group since 2009.

Buchanan grew up in Cincinnati and first came to Africa in 2007 as a student teacher for the Rosslyn Academy, a private Christian elementary and high school in Nairobi, Kenya.

She decided to stay for two years teaching fourth grade, said Dan King, the U.S. manager for the Kenyan school.

Buchanan left the relative safety of Nairobi and began working on land mine education programs in Somalia in May 2010.

"She could hardly talk about Africa without tears in her eyes," said Don Meyer, president of Valley Forge Christian College in Phoenixville, Pa., where Buchanan had studied early education. "This was a deep sense of calling."

She didn't speak to him about the dangers of working in Somalia.

"These kinds of people who serve in these dangerous places, it seems like they don't talk much about the danger," Meyer said.

"Their focus is on their mission. Their safety isn't in the forefront, which amazes me sometimes."